JP4817276B2 - Method for producing porous membrane - Google Patents

Description

【００３６】
【表２】

【００３７】
【表３】

【００３８】
上記結果より、比較例のように圧延前後の厚み変化率が１０より大きく、幅変化率が１．１を超える場合、押出し方向強度および幅方向強度共に変動率が１０％を超えており、シート幅方向における強度バラツキが大きくなっている。これに対して、実施例１や実施例２のように、厚み変化率が１０以下で、幅変化率が１．１以下の場合、押出し方向強度および幅方向強度共に変動率が１０％以下となり、シート幅方向における強度が均一化されている。
【００３９】
このように、圧延前後の厚み変化率と幅変化率とを適切に制御することにより、ＰＴＦＥシートの強度を均一化できることが確認された。従って、実施例１または実施例２に示した方法で製造されたＰＴＦＥシートから得られる製品の物性も安定化することとなる。
【００４０】
【発明の効果】
以上に説明したように、本発明によれば、圧延工程におけるＰＴＦＥシートの強度バラツキの発生を最小限に抑えて、物性の安定したＰＴＦＥシートを提供できる。さらに、ＰＴＦＥシートの物性が安定化することにより、ＰＴＦＥシートから得られる製品の物性も安定化することとなる。
【図面の簡単な説明】
【図１】 本発明のＰＴＦＥシートの製造方法の一実施形態において、一段の圧延ロールを用いてＰＴＦＥ押出し物を圧延する様子を示す模式図である。
【図２】 本発明のＰＴＦＥシートの製造方法の一実施形態において、二段の圧延ロールを用いてＰＴＦＥ押出し物を圧延する様子を示す模式図である。
【符号の説明】
１，１１ 圧延前のＰＴＦＥ押出し物
２，１３ 圧延後のＰＴＦＥシート
３，１４，１５ 圧延ロール
１２ 一段圧延後のＰＴＦＥ押出し物[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polytetrafluoroethylene (hereinafter referred to as “PTFE”) sheet and a method for producing the same, and more particularly to a PTFE sheet useful as a porous membrane, a seal tape, and the like, and a method for producing the PTFE sheet.
[0002]
[Prior art]
PTFE sheets are widely used as substrates for porous membranes, seal tapes, adhesive tapes, and the like. In each such application, the stretchability of the PTFE sheet is used. The PTFE sheet is produced by the following procedure.
[0003]
First, PTFE fine powder and a lubricant are mixed and molded at an appropriate pressure to obtain a preform. Next, the preform is extruded while passing through an orifice to obtain a PTFE extrudate stretched into a rod shape or a ribbon shape. Next, this PTFE extrudate is rolled using a one-stage or multi-stage rolling roll in the extrusion direction to obtain a sheet-like molded article (PTFE sheet).
[0004]
The PTFE sheet produced in this way has high stretchability. Therefore, the PTFE sheet can be used in various applications including a sealing tape and a porous membrane by uniaxially or biaxially stretching at an arbitrary magnification. At this time, making the distribution of physical properties such as strength of the PTFE sheet in all axial directions uniform is effective for stabilizing the physical properties of various products obtained from the PTFE sheet.
[0005]
Japanese Patent Publication No. 42-14178 discloses a method for producing a PTFE extrudate in which elongation in all directions is substantially equal. In this manufacturing method, the physical properties of the PTFE extrudate are stabilized by the shape of the die for obtaining the PTFE extrudate. Japanese Patent Application Laid-Open No. 11-216760 discloses a PTFE extrudate in which local non-uniformity in strength characteristics in the sheet surface is reduced and a manufacturing method thereof.
[0006]
Although the PTFE extrudates produced by these methods have uniform strength and elongation in each direction, the stretching process cannot be performed because the strength in the extrusion direction is low as it is. Therefore, it is necessary to roll this PTFE extrudate using one or more rolls so that the thickness is 1 mm or less. By this rolling process, the orientation of the fibrils in the extrusion direction is moderately generated in the PTFE sheet, and the strength that can withstand stretching is generated. If the stretching process is performed without passing through the rolling process, the PTFE sheet is not sufficiently stretched and breaks due to insufficient strength in the extrusion direction. As described above, the rolling process is an important process that greatly affects the physical properties of the PTFE sheet, similarly to the extrusion process.
[0007]
[Problems to be solved by the invention]
The PTFE sheet produced by the method disclosed in the above publication certainly has uniform strength and elongation at the stage of the PTFE extrudate. However, there has been a problem that the variation in strength is increased by the subsequent rolling process. A PTFE sheet having variations in strength has non-uniform physical properties when stretched, and is not sufficiently stretched and breaks.
[0008]
In order to solve the above problems, an object of the present invention is to obtain a PTFE sheet having stable physical properties while minimizing the occurrence of strength variation of the PTFE sheet in the rolling process.
[0009]
[Means for Solving the Problems]
As a result of intensive studies by the present inventors to achieve the above object, it is clear that the strength variation in the sheet width direction is caused by the flow of PTFE resin in the sheet width direction during rolling. became. That is, when the PTFE extrudate is rolled, the PTFE resin flows not only in the extrusion direction but also in the sheet width direction and the sheet width is expanded. However, the flow of the PTFE resin in the sheet width direction is not restricted. It is an unstable thing. Therefore, as a result, the flow of the PTFE resin in the sheet width direction becomes non-uniform, and the strength varies in the sheet width direction.
[0010]
In order to suppress the occurrence of strength variation due to the flow of the PTFE resin in the sheet width direction, the method for producing a PTFE sheet of the present invention is obtained by extruding a preform including PTFE and a lubricant. In the PTFE sheet manufacturing method including a rolling step of rolling the obtained PTFE extrudate in the extrusion direction,
(Width of PTFE sheet after rolling) / (Width of PTFE extrudate before rolling)
The width change rate before and after rolling defined by is 1.1 or less.
[0011]
By making the width change rate before and after rolling 1.1 or less as in the above method, it is possible to minimize the flow of PTFE resin in the sheet width direction during rolling. As a result, since the occurrence of strength variation in the sheet width direction due to the flow of the PTFE resin in the sheet width direction is minimized, a PTFE sheet having stable physical properties in the sheet width direction can be obtained. Further, by stabilizing the physical properties of the PTFE sheet, the physical properties of the product obtained from the PTFE sheet are also stabilized.
[0012]
Further, in order to suppress the occurrence of strength variation due to the flow of the PTFE resin in the sheet width direction, it is obtained by extruding a preform containing PTFE and a lubricant as a method for producing the PTFE sheet of the present invention. In the PTFE sheet manufacturing method including a rolling step of rolling the PTFE extrudate in the extrusion direction,
(Thickness of PTFE extrudate before rolling) / (Thickness of PTFEEE sheet after rolling)
You may use the method which makes thickness change rate before and behind rolling defined by 10 or less.
[0013]
By setting the thickness change rate before and after rolling to 10 or less as in the above method, the width change rate before and after rolling can be kept low, and the flow of PTFE resin in the sheet width direction can be reduced. As a result, a PTFE sheet having stable physical properties in the sheet width direction can be obtained in the same manner as in the method in which the width change rate before and after rolling is 1.1 or less, and the physical properties of the product obtained from this PTFE sheet are also stabilized. The Rukoto.
[0014]
In addition, as an index indicating the intensity variation, for example, an intensity variation rate is used. The strength variation rate is obtained by taking a plurality of samples in the sheet width direction and using the measured values of the strength. Here, the intensity fluctuation rate of multiple points is
[(Standard deviation of intensity) / (Average value of intensity)] × 100
Defined by
[0015]
Moreover, the PTFE sheet of the present invention is a PTFE sheet produced by rolling an extruded PTFE extrudate, and has a strength variation rate in the sheet width direction of 10% or less.
[0016]
According to such a configuration, the strength variation in the sheet width direction becomes sufficiently small, and the physical properties of the PTFE sheet are stabilized. Thereby, the physical property of the product obtained from a PTFE sheet can be stabilized.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0018]
In the method for producing a PTFE sheet in the present embodiment, a PTFE extrudate is first produced. Specifically, PTFE fine powder and lubricant are mixed and molded at an appropriate pressure to obtain a preform, and then the preform is extruded while passing through an orifice and stretched into a rod or ribbon shape A PTFE extrudate is made. The shape of the PTFE extrudate is not particularly specified, but in order to make the width change rate before and after rolling 1.1 or less in the subsequent rolling process, the cross section is preferably rectangular rather than circular, and the width is increased in thickness. On the other hand, it is more preferable that the ribbon shape is 5 times or more larger.
[0019]
The PTFE extrudate produced in this way is rolled into a sheet using a single or multi-stage rolling roll in a state containing a lubricant. Schematic diagrams showing the rolling process are shown in FIGS. 1 and 2.
[0020]
FIG. 1 shows a state of one-stage rolling in which a PTFE extrudate is rolled using a one-stage rolling roll. As shown in FIG. 1, a PTFE extrudate 1 before rolling having a rectangular cross section is rolled in the extrusion direction by a pair of rolling rolls 3 arranged so that the axial direction is orthogonal to the extrusion direction, and the PTFE sheet 2. It becomes. The rolling direction shown corresponds to the extrusion direction of the PTFE extrudate 1.
[0021]
Further, FIG. 2 shows a state of two-stage rolling in which a PTFE extrudate is rolled using a two-stage rolling roll. As shown in FIG. 2, the PTFE extrudate 11 before rolling having a rectangular cross section is first rolled in the extrusion direction by a first-stage rolling roll 14 arranged so that the axial direction is orthogonal to the extrusion direction. The PTFE extrudate 12 is in a state where the first stage of rolling has been completed. The rolling direction shown corresponds to the extrusion direction of the PTFE extrudate 11. Further, the PTFE extrudate 12 is rolled by a second-stage rolling roll 15 whose axial direction is orthogonal to the extrusion direction and arranged downstream of the first-stage rolling roll 14 in the rolling direction. It becomes.
[0022]
In the present embodiment, the width change rate before and after rolling is set to 1.1 or less. The width change rate before and after rolling is
(Width of PTFE sheet after rolling) / (Width of PTFE extrudate before rolling)
Defined by By controlling the width change rate before and after rolling in this way, the flow of PTFE resin in the sheet width direction (direction perpendicular to the rolling direction) during rolling can be minimized. For this reason, generation | occurrence | production of intensity | strength variation can be suppressed to the minimum and a PTFE sheet | seat with uniform intensity | strength can be implement | achieved.
[0023]
Moreover, in this Embodiment, the gap of a rolling roll etc. are controlled in the case of a rolling process, and the thickness change rate before and behind rolling shall be 10 or less. The thickness change rate before and after rolling is
(Thickness of PTFE extrudate before rolling) / (Thickness of PTFEEE sheet after rolling)
Defined by
[0024]
When the thickness change rate before and after rolling is greater than 10, since the PTFE resin starts to flow in the sheet width direction, the width change rate before and after rolling increases. As a result, strength variation in the sheet width direction occurs. Therefore, as in this embodiment, by suppressing the thickness change rate before and after rolling to 10 or less, the width change rate is suppressed to be low, and the flow of the PTFE resin in the sheet width direction is suppressed. The strength characteristics can be made uniform.
[0025]
The PTFE sheet obtained by the method described above is subjected to steps such as removal of lubricant, sintering, and pore formation by stretching, as necessary. Even after these steps, the strength characteristics of the PTFE sheet become uniform. Therefore, the physical properties of the product obtained from the PTFE sheet produced by the method of the present invention are also stabilized. In the present embodiment, as an index indicating the intensity variation,
[(Standard deviation of intensity) / (Average value of intensity)] × 100
The intensity fluctuation rate defined in is used.
[0026]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples.
[0027]
Example 1
25 parts by weight of liquid paraffin as a lubricant was mixed with 100 parts by weight of PTFE fine powder (CD-123 manufactured by Asahi Glass), and this mixture was preformed into a cylindrical shape. This preform was extruded by a fishtail die (FT die) to obtain a ribbon-like PTFE extrudate. This PTFE extrudate had a width of 80 mm and a thickness of 2.4 mm.
[0028]
The PTFE extrudate as described above was rolled in the extrusion direction with a pair of metal rolling rolls (diameter 400 mm), that is, a PTFE sheet was obtained by one-stage rolling as shown in FIG.
[0029]
In this example, the rolling roll gap was 0.35 mm, and rolling was performed at a roll rotation speed of 2 m / min. The thickness of the PTFE sheet after rolling slightly recovered from the gap to 0.4 mm. The sheet width after rolling was 82 mm. As shown in Table 1, in this example, the thickness change rate before and after rolling was 6, and the width change rate was 1.03.
[0030]
Next, the PTFE sheet rolled as described above was fixed to a metal frame so as not to shrink and left in a dryer at 120 ° C. for 15 minutes to remove the lubricant. The PTFE sheet thus obtained is divided into 10 equal parts in the sheet width direction (the lateral positions 1 to 10 in order from one side), and the strength in the extrusion direction and the width direction is obtained for each sample in the lateral positions 1 to 10. Was measured. The measured intensity, intensity average value, intensity standard deviation, and intensity variation rate are shown in Tables 2 and 3. The sample for strength measurement had a width of 5 mm and a length of 30 mm. In addition, a tensile tester (Shimadzu Autograph AG-1) is used for strength measurement, a tensile force is applied in the length direction of the sample, and the maximum strength until breakage is converted per unit area. It was measured.
[0031]
(Example 2)
In the rolling process of Example 2, the PTFE extrudate was rolled in the same manner as the rolling process of Example 1 except that the gap between the rolling rolls was 0.2 mm. The used PTFE extrudate was also produced in the same manner as in Example 1. In this example, the thickness of the PTFE sheet after rolling was 0.24 mm. The sheet width after rolling was 85 mm. As shown in Table 1, in this example, the thickness change rate before and after rolling was 10, and the width change rate was 1.06.
[0032]
Further, in this example, the strength was measured in the same manner as in Example 1. The measured intensity, intensity average value, intensity standard deviation, and intensity variation rate are shown in Tables 2 and 3.
[0033]
(Comparative example)
In the rolling process of the comparative example, the PTFE extrudate was rolled in the same manner as in Example 1 except that the gap between the rolling rolls was 0.15 mm. The used PTFE extrudate was also produced in the same manner as in Example 1. The thickness of the PTFE sheet after rolling was 0.18 mm. The sheet width after rolling was 90 mm. As shown in Table 1, in the comparative example, the thickness change rate before and after rolling was 13.3, and the width change rate was 1.13.
[0034]
Further, in the comparative example, the strength was measured in the same manner as in Example 1. The measured intensity, intensity average value, intensity standard deviation, and intensity variation rate are shown in Tables 2 and 3.
[0035]
[Table 1]

[0036]
[Table 2]

[0037]
[Table 3]

[0038]
From the above results, when the thickness change rate before and after rolling is greater than 10 and the width change rate exceeds 1.1 as in the comparative example, the rate of change in both the extrusion direction strength and the width direction strength exceeds 10%. The strength variation in the width direction is large. On the other hand, when the thickness change rate is 10 or less and the width change rate is 1.1 or less as in Example 1 or Example 2, both the extrusion direction strength and the width direction strength have a variation rate of 10% or less. The strength in the sheet width direction is made uniform.
[0039]
Thus, it was confirmed that the strength of the PTFE sheet can be made uniform by appropriately controlling the thickness change rate and width change rate before and after rolling. Therefore, the physical properties of the product obtained from the PTFE sheet produced by the method shown in Example 1 or Example 2 are also stabilized.
[0040]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a PTFE sheet having stable physical properties while minimizing the occurrence of strength variation of the PTFE sheet in the rolling process. Furthermore, the physical properties of the product obtained from the PTFE sheet are also stabilized by stabilizing the physical properties of the PTFE sheet.
[Brief description of the drawings]
FIG. 1 is a schematic view showing how a PTFE extrudate is rolled using a single-stage rolling roll in an embodiment of a method for producing a PTFE sheet of the present invention.
FIG. 2 is a schematic view showing how a PTFE extrudate is rolled using a two-stage rolling roll in an embodiment of the method for producing a PTFE sheet of the present invention.
[Explanation of symbols]
1,11 PTFE extrudate before rolling 2,13 PTFE sheet after rolling 3,14,15 Rolling roll 12 PTFE extrudate after one-stage rolling

Claims (1)

Including a stretching step of stretching the polytetrafluoroethylene sheet;
Look including the step of producing by the following production method said polytetrafluoroethylene sheet prior to said stretching step,
The manufacturing method includes:
Including a rolling step of rolling a polytetrafluoroethylene extrudate obtained by extruding a preform made of polytetrafluoroethylene fine powder and a lubricant into a ribbon shape in the extrusion direction;
(Width of polytetrafluoroethylene sheet after rolling)
/ (Width of polytetrafluoroethylene extrudate before rolling)
A method for producing a porous film, wherein the rate of change in width before and after rolling defined by is 1.1 or less .

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